1. Field of the Invention
The invention relates to a catadioptric projection objective for microlithography, with at least one curved mirror, and an operating process that increases image quality of such an objective
2. Discussion of Relevant Art
U.S. Pat. No. 5,142,132 describes a wafer stepper with an objective of this field and a planar mirror that can be deformed by an x-y array of actuators in order to correct optical errors. As large as possible a number of actuators for respectively a smallest possible portion of the mirror is described as advantageous. The adjustable mirror is driven at a large angle of reflection so that its effects are severely asymmetrical.
Projection objectives for microlithography having elements whose position can be varied (z-drive) or with change of the optical path by change of pressure or of the composition of the filling gas are known in different variants with many kinds of control circuits. Purely refractive objectives are described here as a rule.
European Patent EP 0 660 169 describes a refractive projection objective for microlithography with correction by rotation of cylindrical lenses of errors that are not rotationally symmetrical. Citations relating to longitudinally displaceable lenses are also described.
Catadioptric projection objectives with a curved mirror and a polarization beam splitter are known, e.g. from German Patent DE 196 16 922.4 (U.S. patent application Ser. No. 08/845,384 filed Apr. 15, 1997) and the citations given therein. The content of this patent application is incorporated herein by reference.
Other catadioptric projection objectives are likewise known, e.g., those of the type of the modified Schupman achromats, also termed H-design, and described, e.g., in U.S. Pat. No. 5,052,763.